1. Field of the Invention
The present invention relates to a motor drive circuit that is provided with a failure detection function in a circuit in which a return current element is connected in parallel to a motor.
2. Description of the Related Art
A known motor drive circuit is disclosed in Japanese Patent Application Publication No. JP-A-2001-511636 in which a freewheeling diode that serves as a return current element is connected in parallel to both terminals of a motor that is provided for a brake fluid pressure control actuator or the like. In this sort of motor drive circuit, in a case where the motor is driven by PWM, when a surge is generated by a back electromotive force that is generated when the PWM drive is off, the surge can be directed through a return current circuit through the freewheeling diode that is connected in parallel to the motor, making it possible to suppress the surge.
Furthermore, in the motor drive circuit with this sort of structure, in a case where a battery is connected in reverse, the freewheeling diode is connected in the forward direction, making it possible for a short-circuit current to flow. A diode for protecting the freewheeling diode against a reverse connection is therefore connected in series to prevent the short-circuit current when the battery is connected in reverse.
In the known motor drive circuit described above, an initial check for a failure location is performed. The initial check may be conducted, for example, by turning on and off a semiconductor switching element that controls an electric current supply to the motor.
However, it is not possible for an initial check described above to check for a fault in which the freewheeling diode is open (short-circuited), so it is not possible to detect a failure in the return current circuit that is due to the freewheeling diode. Therefore, in the worst case, the back electromotive force that is generated when the motor is turned off will destroy the semiconductor switching element.